The invention relates to a braking pressure modulator.
German patent document DE 42 27 084 A1 discloses a braking pressure modulator, designated therein as a pressure regulating module.
This known patent shows a two-channel pressure regulating module in FIG. 2 in which a common 3/2-way solenoid valve (therein 12) is provided as a reversing valve that connects both channels via a line (therein 15) either to the supply pressure (therein 17) in the actuated state of the valve 12, or to a control pressure (therein 13) in the non-actuated state of the valve 12. For purposes of this discussion, it shall be assumed that the 3/2-way solenoid valve 12 of DE 42 27 084 A1 is actuated, so that the supply pressure is being supplied to the other solenoid valves in FIG. 2. This represents the case of pressure regulation.
One of the two symmetrically configured pressure regulating circuits in DE 42 27 084 A1, i.e., the one containing the valves 9xe2x80x2, 7 and 3, is now considered. The 3/2-way solenoid valve (therein 9xe2x80x2) determines the direction of any pressure change in this circuit. In the non-actuated state of valve 9xe2x80x2 (as shown in FIG. 2 therein), a pressure increase takes place in this circuit since the supply pressure 17 is taking effect. In the actuated state of valve 9xe2x80x2, a pressure lowering takes place due to the connection of valve 9xe2x80x2 to the exhaust (therein 11xe2x80x2). The 2/2-way solenoid valve (therein 7) is connected in series to the valve 9xe2x80x2 and either establishes a connection to a control inlet of the downstream relay valve (therein control inlet 5) in its non-actuated state (as shown in FIG. 2), or closes off this control inlet in its actuated valve position.
Due to the series connection of the two valves 7 and 9xe2x80x2, these must jointly be brought into a given state in order to achieve a desired pressure change at the control inlet 5. Thus, they are not independent of each other but can only be operated simultaneously and together. This represents a cost disadvantage because the utilization of a 3/2-way solenoid valve with reversing function (i.e., valve 9xe2x80x2), and the requirement of great tightness in fitting at the two corresponding valve seats, are relatively expensive.
When using the 3/2-way solenoid valve 9xe2x80x2 as a reversing valve, a velocity disadvantage manifesting itself by a reduced actuation rate occurs because of the usual design of 3/2-way solenoid valves which have elastomer sealing seats provided at the armature for both switching positions.
It is therefore the object of the present invention to modify a pre-engagement unit of a braking pressure modulator of the type mentioned initially in such manner that the time response will be improved.
This object is achieved by a pre-engagement unit for a braking pressure modulator for a pressure regulating circuit of an electronic braking system of a vehicle, the pre-engagement unit including a first pneumatic inlet through which a supply pressure is supplied to the pre-engagement unit, a second pneumatic inlet through which a redundancy pressure is supplied to the pre-engagement unit, a first pneumatic output terminal through which the pre-engagement unit is connected to an air quantity augmenting relay valve, and a second pneumatic output terminal through which the pre-engagement unit is connected to a pressure sink. The pre-engagement unit also includes an electrically actuated valve system having a plurality of solenoid valves including a plurality of electrical terminals which are connected to output terminals of an electronic control unit. An electric braking command signal transmitter of the vehicle delivers a driver initiated electric brake value setting to an input of the electronic control unit. Under normal conditions, both the supply pressure and the redundancy pressure are delivered at the first pneumatic output terminal to be converted by the air quantity augmenting relay valve to a braking pressure determined by the electric brake value setting. In the case of a failure in the electronic braking system, the redundancy pressure is delivered at the first pneumatic output terminal to be converted by the air quantity augmenting relay valve to the braking pressure.
Due to the fact that with the invention the pressure is influenced by the redundancy pressure at the pneumatic output terminal of the pre-engagement unit even in normal operation, the advantage is created that the pressure build-up is accelerated in case of full braking and that the pressure reduction is shortened in case of ABS braking.
Further developments of the invention that concern the pneumatic circuit of the pre-engagement unit have the advantage of reduced manufacturing costs.
In the patent document DE 42 27 084 A1, the suggestion is made through various embodiments to achieve economy by reducing the number of solenoid valves and thereby to save on pneumatic channels and similar components. The present invention abandons the idea to a great extent that the number of solenoid valves as such is the most important factor in saving costs. In the present invention, the average number of 3 solenoid valves per channel is even slightly greater than the average number of 2.5 solenoid valves per channel in the known patent. Instead, the invention emphasizes a novel valve design and a pneumatic circuit by means of which the solenoid valves of this novel valve design can be operated optimally.
In a further development of the invention, in which a solenoid valve provided for pressure increase in the pre-engagement unit is connected in parallel to a solenoid valve provided for pressure reduction, the advantage is obtained that the two valves can be actuated simultaneously. By selecting different nominal values and the possibility to use both valves at the same time or only one at a time for pressure modulation, great precision or high speed pressure modulation can be obtained. It is also possible to obtain both high speed and great precision in pressure modulation.
A further development of the invention has the advantage that the armatures can be made in a particularly space-saving configuration by employing sealing seats that form metal-to-metal seals when the solenoid valves are under current. The solenoid valves switch very rapidly thanks to their short strokes. Because of these short strokes and the low demands made upon the armature force, the magnet coils producing the magnetic force and thereby the entire construction unit can be kept small.
In another further development of the invention, the armatures of the solenoid valves are standardized, and by using identical armatures manufactured in large quantities, costs are reduced.